Expanding hollow plastic posts on opposite sides of electrode apertures for gripping electrodes



May 9, 1967 M, DREES 3,317,981

EXPANDING HOLLOW PLASTIC POSTS ON OPPOSITE SIDES OF ELECTRODE APERTURES FOR GRIPPING ELECTRODES Filed Nov. 18, 1965 22 |5 22 n (my I5 I I I5 I50 I LE I 1233i I f-Isa w I 'i East-4e 1 In I I I (6:25 A; 20 I9 I6 J 1: 2 H K I h I: J 5 24 I 2| in IS I lOb I log I0 INVENTOR.

'50 JOSEPH M. DREES wit-g 2 ATTORNEY United States Patent EXPANDING HOLLOW PLASTIC POSTS 0N 0P- POSITE SIDES OF ELECTRODE APERTURES FOR GRIPPING ELECTRODES Joseph M. Drees, Saratoga, Calif., assignor to Sylvanra Electric Products Inc., a corporation of Delaware Filed Nov. 18, 1963, Ser. No. 324,267 4 Claims. (Cl. 29-2513) This invention relates to gun structures for electron discharge devices such as cathode ray tubes and traveling wave tubes, and more particularly to an improved gun structure and method of assembling and securing axially aligned and spaced electrodes in such a gun structure.

Electrodes in electron gun assemblies generally must be axially spaced and aligned as well as electrically insulated from each other. A common practice of so supporting these electrodes is embedding tabs on the electrodes into heat-softened glass rods or beads which then cool and harden to permanently secure the parts together. The embedding step is a separate mechanical operation, generally accomplished either by building up the glass insulator stubs on the tabs as by using a glass cane as a welding rod, or by pressing the tabs into a heated glass stub. This step is repeated at three or more peripherally spaced points around the stacked electrodes, each stub being attached one at a time. Not only is this time consuming, but independent heating of one part of the gun structure while the other parts are cool tends to upset alignment of the electrodes or to unduly stress them and the stubs so as to render the gun structure susceptible to damage and breakage.

In accordance with this invention, the mechanical connection of all the insulator posts to the electrodes takes place simultaneously and somewhat automatically. The posts comprise hollow tubes of glass or the like hermetically sealed at opposite ends so as to define a closed chamber within each post. The electrodes are formed with support openings which are axially aligned to receive the posts. With the posts in the openings and with the electrodes aligned and spaced, the assembly is uniformly heated in an oven. The walls of the posts soften and the increased pressure in the post chambers expands the Walls into tight engagement with the electrodes. When the posts cool, the connection becomes permanent.

An object of this invention is the provision of a gun assembly with insulator spacer-posts so attached to the electrodes as to minimize distortion and stress of the gun parts.

Another object is the provision of a method of fabricating an electron gun assembly without inducing thermal stress in the electrodes or insulators.

A further object is the provision of a technique for securing a plurality of insulator posts to gun electrodes in one heating operation.

These and other objects of the invention will become apparent from the following description of a preferred embodiment thereof reference being had to the accompanying drawings in which:

FIGURE 1 is a section of completed electron gun assembly embodying the invention taken on line 1-1 of FIGURE 2;

FIGURE 1-A is a section of part of an uncompleted gun assembly showing an insulator post in position prior to the firing operation; and

FIGURE 2 is a transverse section taken on line 22 of FIGURE 1.

Referring to the drawings, an embodiment of the invention is shown as a gun assembly comprising a cathode assembly 10, first and second planar electrodes 11 and 12, respectively, and a third cylindrical electrode 13.

3,3 l 7,98 l Patented May 9, l 967 Cathode assembly 10 and the three electrodes are supported symmetrically about axis A of the assembly at predetermined axially spaced positions by a plurality of substantially identical tubular insulator posts 15 having inner chambers 15a. Electrodes 11 and 12 have central apertures 16 and 17, respectively, with axes coincident with the gun axis A and similarly the axis of cylindrical electrode 13 is coincident with axis A. Cathode assembly 10 has an outer cylindrical shield 10a and an inner body 10b comprising an emitting surface 19 from which electrons are directed along the axis of the assembly through the electrode apertures. Electrical leads, not shown, are connected to the electrodes to provide appropriate electrostatic fields for shaping and accelerating the electron beam. Typically, electrodes 11 and 12 may be control grids and electrode 13 an accelerator grid in a cathode ray tube.

Cathode assembly 10- is supported on posts 15 by an annular support ring 20 secured as by welding to a flange 21 on outer shield 10a and electrode 13 is similarly supported on the posts by ring 22 permanently secured to the side of the electrode.

The peripheral edge portion of support ring 20, electrodes 11 and 12, and support ring 22 are formed with sets 24, 25, 26 and 27 respectively, of support openings equally radially spaced from axis A. The electrodes are angularly oriented relative to each other so that the support openings in each electrode and support ring are aligned with the other sets of support openings. Each post 15 extends through an aligned series of these support openings and projects above and below (as viewed) support rings 20 and 22.

The posts are substantially identical and preferably are made of thin-wall glass or other similar insulator material which softens when heated to a predetermined temperature, preferably as low as possible for guns in cathode ray tubes. The diameter of each expanded post between electrodes in a finished gun assembly is substantially greater than the diameters of the support openings, and the portion of the post which extends through each opening presses tightly against the side of the opening. Accordingly, the opposite side surfaces of each support ring and electrode adjacent the support opening therein are engaged tightly by overlying portions of the post which therefore firmly binds the engaged portions and prevents any axial or other displacement of electrodes relative to each other.

The method of assemblying the gun structure will now be described. After rings 20 and 22 have been secured to cathode shield 10a and electrode 13, respectively, and central apertures 16 and 17 have been formed in elec trodes 11 and 12, support openings 24, 25, 26 and 27 are formed in these parts preferably on concentric centers. The electrodes are next accurately aligned along axis A as by mounting them on an axially true mandrel which extends through the central openings in the electrodes and cathode shield 10a. To accommodate the different center opening diameters, an adapter having a center opening equal in size to apertures 16 and 17 may be temporarily secured to each of electrode 13 and shield 10a for receiving a straight cylindrical mandrel. Ceramic spacers or the like are placed between the electrodes to establish proper interelectrode spacing and parallelism and the electrodes are angularly adjusted to align the support openings. Elongated straight tubular insulator posts 15, see FIGURE l-A, having external diameters slightly less than those of the support openings, are then inserted through those openings in the respective electrodes. In guns for most cathode ray tube applications, commercial glass tubing is satisfactory.

Each post 15 is somewhat longer than the axial spacing between opposite end electrodes to be supported. The open post ends are hermetically sealed by local heating preferably before the posts are inserted into the openings. Chamber a in each post is therefore completely sealed.

The assembly is next placed in an oven and is heated rapidly to a predetermined temperature at which the post walls begin to soften. In accordance with the invention, the pressure within post chambers 15a increases substantially with the increase in temperature and causes the softened elastic post walls to expand sufficiently to tightly grip each electrode at and adjacent to the support openings therein. The temperature of the oven is maintained substantially constant for a predetermined time to insure proper expansion of all posts. Thereafter the oven is cooled and the posts simultaneously harden to rigidly mechanically grip the electrodes. The spacers, mandrel and adapters are removed and the cathode body 10b and electrical leads are connected to complete the assembly. It will be noted that the axis of shield 10a is colinear with the axis of electrodes 11, 12 and 13 and provides an accurate reference as well as support for cathode body 10b.

If desired, the posts may be filled with a suitable material such as low temperature potting compound to increase the strength and rigidity of the gun assembly.

Changes, modifications and improvements may be made to the above described method and embodiment of the invention without departing from the principle and precept thereof. The appended claims therefore describe the invention in terms consistent with the extent to which it has advanced the art.

What is claimed is:

1. The method of assembling an electron gun having a plurality of electrodes consisting of the steps of aligning and spacing the electrodes along an axis,

inserting end-sealed tubular thermo-plastic posts through aligned openings in said electrodes, heating the electrodes and posts to a temperature at which the post walls soften and the pressures within the posts increase to cause said walls to expand whereby to grip the electrodes at the openings, and

cooling the assembly whereby the posts harden in their expanded state.

2. The method of assembling an electron gun having a plurality of electrodes with central apertures and a tubular cathode element for supporting an electron emitter consisting of the steps of stacking said electrodes and said cathode element with a predetermined spacing therebetween and with the axes of said central apertures and said cathode element in alignment,

disposing each of a plurality of elongated hollow sealed thermo-plastic posts against a portion of each of said electrodes and cathode element,

uniformly heating the posts, electrodes and cathode element until the .post walls become elastic and the pressures within the posts increase to cause said walls to expand outwardly into tight engagement with adjacent parts of the electrodes and cathode element, and

cooling the assembly uniformly and allowing the post walls to harden in their expanded state whereby to permanently grip the electrodes and cathode element. 3. The method of assemblying an electron gun having a plurality of electrodes with central apertures and a cylindrical cathode element, each of said electrodes and cathode element having an annular portion formed with a plurality of support openings, the method consisting of the steps of inserting a mandrel through said central apertures of the electrodes and through the cathode element for aligning the axes of the apertures and of the element,

axially spacing and angularly adjusting said electrodes and said cathode element on said mandrel until the support openings of each are aligned with the other to form a plurality of aligned series of openings,

inserting a hollow glass post through each series of support openings,

hermetically sealing opposite ends of each glass post to define therewit-hin a closed chamber with a pressure which increases when heated,

heating the assembly in an oven until the walls of the posts soften and the increased pressure within the posts causes the post walls to expand into engagement with said annular portions at the support openings,

uniformly cooling the assembly and allowing the post walls to harden simultaneously in the expanded state, and

removing said mandrel.

4. The method of supporting a plurality of longitudinally spaced elements with a thermo-plastic tubular post, each of said elements having at least one support opening therein, consisting of the steps of hermetically sealing opposite ends of said post and thereby defining therewithin a closed chamber with a pressure that increases when heated,

aligning the support openings in said elements,

inserting said post through said aligned support openings,

heating said post to a temperature at which the post wall becomes elastic and the pressure in the chamber increases sufficiently to expand said wall tightly against the elements at the openings, and

cooling the post and allowing the wall thereof to harden in the expanded state.

References Cited by the Examiner UNITED STATES PATENTS 2,153,223 4/1939 Young 313-82 2,195,914 4/1940 Baier 313-82 3,016,471 1/1962 Drake et a1 3l3-82 FOREIGN PATENTS 630,136 10/1949 Great Britain.

JAMES W. LAWRENCE, Primary Examiner, ROBERT SEGAL, Examiner, 

1. THE METHOD OF ASSEMBLING AN ELECTRON GUN HAVING A PLURALITY OF ELECTRODES CONSISTING OF THE STEPS OF ALIGNING AND SPACING THE ELECTRODES ALONG AN AXIS, INSERTING END-SEALED TUBULAR THERMO-PLASTIC POSTS THROUGH ALIGNED OPENINGS IN SAID ELECTRODES, HEATING THE ELECTRODES AND POSTS TO A TEMPERATURE AT WHICH THE POST WALLS SOFTEN AND THE PRESSURES WITHIN THE POSTS INCREASE TO CAUSE SAID WALLS TO EXPAND WHEREBY TO GRIP THE ELECTRODES AT THE OPENINGS, AND COOLING THE ASSEMBLY WHEREBY THE POSTS HARDEN IN THEIR EXPANDED STATE. 